1. Field of the Invention
The present invention relates to improved collection structures for collecting electrical energy in batteries, e.g., a lithium-ion battery, and relates in particular to an electrode which has an electrically conductive carrier foil having a terminal region for connection to an electrical circuit, and in which, in order to improve electrical collection via the terminal region, the carrier foil has at least one electrically conductive structure element by way of which the electrical resistance between the terminal region and a point on the carrier foil is decreased.
2. Description of the Related Art
In order to manufacture batteries such as, for example, lithium-ion batteries, an active layer is applied onto an electrically conductive collector. For example, graphite-containing pastes or nanocrystalline amorphous silicon having lithium inclusions, or also lithium mixed oxides such as Li4Ti-5O12, LiCoO2, LiNiO2, LiMn2O4, lithium iron phosphate (LiFePO4), or tin dioxide (SnO2) can be applied as an active layer onto a carrier foil serving as a collector. Copper foil or aluminum foils can be used, for example, as carrier foils. It is also known to use networks or foams made of, for example, nickel as carrier foils. Coated carrier foils of this kind are assembled as an anode and/or cathode to form a battery, and incorporated into a package, a separator being provided between the anode and cathode. The package can be embodied as a pouch, layer being placed upon layer in sandwich fashion (e.g. anode-separator-cathode) and a usually square packet being constituted. Alternatively, an anode-separator-cathode unit can be rolled up, thus yielding the cells known, for example, from the laptop computer sector.
The packages thereby obtained are filled with an electrolyte. Suitable electrolytes are, for example, salts such as LiPF6 or LiBF4 in anhydrous aprotic solvents such as, for example, ethylene carbonate or diethylene carbonate, etc. Also suitable are polymers made up of polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-hexafluoropropene (PVDF-HFP), as well as Li3PO4N (lithium phosphate nitride). These can be present and introduced both in liquid form and as a gel or solid.
A cell of this kind can be electrically contacted via an electrically conductive collector, which must have a cross section sufficient for the current intensity that needs to be handled.
As a rule, multiple small cells are connected together, with a high degree of wiring complexity, for a high-performance overall system. An alternative possibility, in order to avoid such wiring complexity, is to produce correspondingly large-area electrodes.
The difficulty then exists, during the charging and discharging of such a battery, that the current generated incrementally in the surface area of the electrode flows out of all regions of the electrode toward the collector. The result is that the current density in the electrode rises continuously in the direction of the collector.
Electrical conduction is often associated with losses, which become evident as local heating of the battery. Defects in the ideal disposition, for example an irregular coating, excessively large particles in the layer, inhomogeneous compression of the electrodes, or the like, result additionally in an inhomogeneous current flow in the electrode. Local or zonal overheating of the battery can therefore occur; this can result in premature aging, capacity loss, or even thermal damage to the battery.